Based on some of our past project experience, we have found that there tends to be a considerable amount of confusion and uncertainty surrounding the requirements for atrium based smoke control systems. This article serves to provide some clarity on the technical and code requirements of these systems. It should be understood that the underlying intent of a smoke control system is to provide a safe and clear means of egress from the Atrium for the building occupants.
An atrium is defined as an opening connecting two or more stories (excluding stairwells, elevators, escalators, and MEP shafts). Note that atriums for malls have a separate set of requirements all together. The International Building Code (Section 404) determines that a smoke control system is required for all atriums open to three or more stories, except for Institutional classifications I-1 (rehabilitation, treatment centers, etc.) and I-2 (hospital, nursing homes, assisted living), which require smoke control at two or more stories. Where IBC determines that a smoke controls system is required, we must refer to the specific requirements as defined within Section 909.
Smoke control systems are not intended to preserve building contents, or allow timely restoration of operations, or assist in the fire suppression activities. Section 909, smoke control systems requirements, provide a life safety imperative, being establishment of a tenable environment for the evacuation or relocation of occupants during a fire event.
Section 909 requires designs for smoke control be in accordance with generally accepted and well established principals of engineering. It also requires design documents to describe adequately the elements of design including necessary information and analysis to demonstrate compliance. The section also obligates the designer to specify the post installation special inspections and testing to verify proper commissioning of the system.
It is important that both the design and testing of the smoke control systems be performed by qualified, registered professionals. Submission of a smoke control system design requires an additional “rational analysis” document that must reflect consideration in the design of a minimum of seven (7) different factors including stack effect, temperature effects of fire, wind effects, other HVAC system interactions, and effects of climate on system operation.
Section 909 goes on to outline requirements for the atrium to be provided with smoke barriers. The smoke barriers section prescribes a maximum leakage of the space though gaps around doors and operable windows. This section of the code goes on to detail the permissible methodologies for designing a smoke control system which include the pressurization method, airflow design method, and the exhaust method.
The pressurization method involves supplying large amounts of air into an atrium, usually from the bottom of the space, with pressure relief vents at the top. This method is typically employed in stairwells and smaller enclosed egress passages. The airflow design method is a passive technique utilizing a pressure relationship between fixed openings where smoke is directed away from the fire. The exhaust method uses mechanical exhaust with make-up air openings to draw smoke out of the atrium. This is the most commonly employed methodology in commercial atrium applications.
The rational analysis, required by the IBC, typically includes a computerized model that simulates a design fire (including fuel and location) and estimates the amount of smoke and heat release as well as considerations for sprinkler impacts. This analysis will be used to determine the ventilation rates required to maintain the safe egress conditions in the exit path. The analysis also identifies locations for exhaust fans and make-up air sources, as well as means of minimizing smoke migration to communicating spaces.
Once the system parameters are established, the requirements of NFPA must be integrated into the detailed design. Some of these factors include integration with the fire alarm system and triggering smoke detectors, implementation and control of smoke control dampers, limiting air flow in egress paths to 200 FPM, fire fighter’s smoke control station, limiting pressure differences across atrium to .05″, and interlocking any HVAC equipment not related to the smoke control system.
Once the system is designed and installed, special inspections and testing per IBC Section 1704 are performed. This test is typically witnessed by the AHJ and the design engineer. A report is submitted to the AHJ for final approval.
As can be observed by this article, these system designs are complicated and require an extensive amount of engineering analysis before a design is even started. The rational analysis requirement provides an opportunity to optimize the system sizing and potentially save money on the installation cost of this system. The regulatory and approval requirements require these fully engineered systems to be carefully designed and constructed to ensure that the system is accepted by the AHJ.
Engineering Humor
Summer Vacation Job
The boys were arriving back at the fraternity house after the summer vacation.
“What have you been doing this summer?” one asks another.
“Working in my dad’s office, and you?”
“Yeah, I’ve been loafing around and doing nothing too.”
Paying Taxes
A nervous taxpayer was unhappily conversing with the IRS Tax auditor who had come to review his records.
At one point the auditor exclaimed, ”Mr. Carelton, we feel it is a great privilege to be allowed to live and work in the USA. As a citizen you have an obligation to pay taxes, and we expect you to eagerly pay them with a smile.”
”Thank goodness,” returned Mr. Carelton, with a giant grin on his face, ”I thought you were going to want me to pay with cash.”
In What Gear
ATTORNEY: What gear were you in at the moment of the impact?
WITNESS: Gucci sweats and Reeboks.
Wake-up Call
Here’s a little tip from me to you as an experienced traveler. Wake-up calls are the worst way to wake up. The phone rings, it’s loud and you can’t turn it down. I leave the number of the room next to me. It just rings very quietly and you hear a guy yell, “Why are you calling me?” Then I get up and take a shower. It’s great.
Sick On Weekdays
My boss said, “I find it highly suspicious that you are only sick on weekdays.”
I said, “It must be my weekend immune system.
Witness Required
Top 3 situations that require witnesses:
1) Crimes
2) Accidents
3) Marriages
Need I say more?